1. Field of the Invention
Apparatuses consistent with the present invention relate to a perpendicular magnetic recording medium, and more particularly to a perpendicular magnetic recording medium, which can restrain formation of multi granule domains, thereby minimizing noise of a soft magnetic under-layer.
2. Description of the Prior Art
Generally, perpendicular magnetic recording mechanisms have a higher recording density than that of longitudinal magnetic recording mechanisms. Therefore, the latest hard disc drive employs a perpendicular magnetic recording mechanism for the high recording density.
In the perpendicular magnetic recording mechanism, magnetization is accomplished perpendicular to a plan surface of a medium. Such a perpendicular magnetic recording mechanism includes a perpendicular magnetic recording medium having a double magnetic layer with a ferro-magnetic layer and a soft magnetic under-layer, and a pole head.
Hereinafter, the configuration of the related art perpendicular recording medium will be described with reference to FIG. 1.
FIG. 1 is a view showing a configuration of a laminated perpendicular magnetic recording medium according to a related art. As shown in FIG. 1, the related art perpendicular magnetic recording medium respectively includes a substrate 1, a soft magnetic under-layer 3, an intermediate layer 5, a perpendicular magnetic recording layer 7, and a protection layer 9, which are in turn laminated.
The substrate 1 is mainly made of glass or AlMg, an alloy of Aluminum (Al) and Magnesium (Mg), and the soft magnetic under-layer 3 made of CoZrNb, an alloy of Cobalt (Co), Zirconium (Zr), and Niobium (Nb), CoFeB, an alloy of Co, Iron (Fe) and Boron (B), or NiFe, an alloy of Nickel (Ni) and Fe. The intermediate layer 5 is substantially formed from Tantalum (Ta)/Ruthenium (Ru), the perpendicular magnetic recording layer 7 made of CoCrPt—SiO2 and the like, and the protection layer 9 made of Diamond Like Carbon (DLC).
In order to increase a field strength and a field gradient during recording of data on the perpendicular magnetic recording medium, the soft magnetic under-layer 3 must be prepared under the perpendicular magnetic recording layer 7 in character of the magnetic circuit of a pole head. However, the soft magnetic under-layer 3 generates a magnetic flux as noise caused by a domain wall. Accordingly, there is a problem in that the soft magnetic under-layer 3 acts as a noise source when data is reproduced.
As shown in FIG. 1, if the perpendicular magnetic recording medium has a simple configuration, it is impossible to prevent the soft magnetic under-layer 3 from making multi-domains. The multi-domains of the soft magnetic under-layer 3 act as a factor of remarkably decreasing a Signal to Noise Ratio (SNR) when data is reproduced. In the case of the perpendicular magnetic recording medium with a high density, reduction of a SNR caused by the multi-domains of the soft magnetic under-layer is very serious.
Thus, many methods have been researched in order to solve the problem of generation of noise due to the multi-domains. Specifically, there has been proposed a perpendicular magnetic recording medium having a structure in which the soft magnetic under-layers with a single domain are interposed between the substrate and the perpendicular magnetic recording layer.
Where a plurality of soft magnetic under-layers is interposed between the substrate and the perpendicular magnetic recording layer, it is possible to restrain noise caused by the multi-domains. However, there are problems in that processes are complicated, productivity is lowered, and manufacturing costs increase.
Meanwhile, a magnetic domain with a size of nanometer scale has been proposed to reduce noise of a soft magnetic under-layer. Japanese Laid-open Patent Publication No. 2004-079104 discloses a high dense magnetic recording medium including a non-magnetic substrate 11, a soft magnetic material layer 13 formed on the non-magnetic substrate 11 and having nanoparticles 13′, an intermediate layer 15 formed on the soft magnetic material layer 13, and a hard magnetic material layer 17, as shown in FIG. 2.
In the high dense magnetic recording medium according to the Japanese Laid-open Patent Publication 2004-079104, it is possible to control the generation of noise due to the irregular diameter of particles by controlling uniformly the mean diameter of the nanoparticles which are dispersed in the soft magnetic material layer. However, the nanoparticles still interact with one another. Further, the nanoparticles, which are magnetized in the same direction, are located adjacent to one another so as to form multi granule domains. Therefore, it is difficult to restrain the generation of noise due to the form of the multi granule domains in the soft magnetic material layer.